Abstract
Microalgae are promising candidates for biofuel production due to their high lipid content. To facilitate utilization of the microalgae for biofuel, rapid quantification of the lipid contents in microalgae is necessary. However, conventional methods based on the chemical extraction of lipids require a time-consuming destructive extraction process. Here, we demonstrate label-free, non-invasive, rapid quantification of the lipid contents in individual micro-algal cells measuring the three-dimensional refractive index tomograms. We measure three-dimensional refractive index distributions within Nannochloropsis oculata cells and find that lipid droplets are identifiable in tomograms by their high refractive index. In addition, we alter N. oculata under nitrogen deficiency by measuring the volume, lipid weight, and dry cell weight of individual cells. Characterization of individual cells allows correlative analysis between the lipid content and size of individual cells.
Highlights
Biofuels have attracted increasing attention as sustainable energy resources that could potentially replace fossil fuels
Optical diffraction tomography (ODT) or holotomography has emerged as a technique to provide quantitative three-dimensional (3D) imaging of biological samples without exogenous agents[16,17,18,19,20]
By measuring 3D refractive index (RI) tomograms of living microalgae (Nannochloropsis oculata) we show that the lipid content in cells can be identified and quantified from the distinctively high RI values of the lipids
Summary
Biofuels have attracted increasing attention as sustainable energy resources that could potentially replace fossil fuels. Among the candidates suggested for biofuel production are a variety of plants[1,2], fungi[3], bacteria[4,5], and microalgae[6] The latter has long been considered a promising sustainable resource due to their rapid growth and high lipid content[7,8]. We present label-free, non-invasive, quantitative measurements of lipid content in individual micro-algal cells using ODT (Fig. 1 and Materials and Methods). The label-free quantitative imaging capability of ODT presents a promising potential breakthrough for industrial quantification of lipids, as well as providing a useful imaging technique for biological research to investigate the physiology of many kinds of living cells
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